don't prepend raw close code anymore

thanks to recent crystal changes adding support for close reasons we
don't need to encode things anymore.

src/kemal/websocket.cr

@@ -50,11 +50,9 @@ module Kemal
             message = "Exception"
           end
 
-          raw = uninitialized UInt8[2]
-          IO::ByteFormat::BigEndian.encode(code, raw.to_slice)
           socket.not_nil!.close(
             HTTP::WebSocket::CloseCode.new(code),
-            message: String.new(raw.to_slice) + message
+            message: message
           )
 
           raise error unless error.is_a?(WebsocketError)